Wastegates for exhaust turbines may be internal or external with respect to a turbine housing. For example, an external wastegate valve may be mounted in an exhaust conduit upstream of a turbine housing to allow for exhaust gas to bypass a turbine wheel housed by the turbine housing. For vehicles with internal combustion engines, such an approach requires additional space in an engine compartment between an engine block and the turbine housing to mount the external wastegate valve and associated piping. In contrast, an internal wastegate valve is at least partially integrated into a turbine housing and may be configured to require no additional piping. For example, a turbine housing with an internal wastegate valve may be provided with a poppet that can open and close to control exhaust flow in a passage leading to a turbine wheel space where, for a closed state, exhaust entering the turbine housing is directed to the turbine wheel space and, for an open state, at least some gas entering the housing bypasses the turbine wheel space (i.e., so-called “wastegating”).
As exhaust turbines may operate at quite high temperatures, often turbine housings are made from iron or an alloy with significant iron content (e.g., stainless steel). For cast iron turbine housings, features to accommodate an internal wastegate valve can add significant mass, which, in turn, can reduce fuel economy for a vehicle that must move the additional mass. Consequently, some efforts have been made to construct turbine housing from aluminum alloys in an effort to reduce mass.
Apart from the traditional challenges related to turbine housing durability (e.g., due to fatigue, cracking, creep, etc.), additional challenges exist for aluminum alloy turbine housings. A primary concern is temperature, which may be addressed by water cooling. For example, an aluminum alloy turbine housing may include its own water cooling passages or, for example, features that allow for mounting of an external cooling jacket to the housing. For aluminum alloy turbine housings with internal wastegate features, another concern relates to interaction with standard wastegate parts (e.g., as used in stainless steel turbine assemblies). A particular concern relates to behavior of an aluminum alloy turbine housing upon contact with a wastegate valve poppet.
Various techniques, technologies, etc., described herein provide for an aluminum alloy turbine housing with a valve seat having one or more properties for compatibility with a poppet. Such a valve seat may improve durability with respect to interactions with a poppet, whether during periods of operation (e.g., where exhaust flows to the housing) or even optionally during periods of non-operation (e.g., a cool-down period following use, a period of non-use, a storage period, etc.).